You're safe if you make sure to always localize $SWAP and make sure it's what you want it to be. Admittedly that adds needless red tape. I am really opposed to making such distinctions by letter case though - there's just no criterion for why it's the capitalized version that does it that way around, and not the lowercase.

As far as the ordering is concerned, I believe you should just learn it, yes. :) It follows the convention of most every other comparable function: link, symlink, rename etc all take the source as first and the target as second argument.

Makeshifts last the longest.